Yes, just let them eat. As they never have that kind of food before so they will eat as much as they can, but after few month or one year, they found out that they gave many weight, then they will lose weight and control herself. My first maid was like that.
My current maid, CV mentioned she is 56 kgs, when she arrived HK, her weight is 67kgs ah. Now she also eat a lot.
As long as she can finish all works properly, i don't care what she eat.